Question

我有一个从Swift调用的c函数，但我认为应该可以在Swift中实现，诀窍是能够将float数组的内存转换为simd_float4数组。下面是我的c函数以及如何在Swift中调用它

迅速

sumFloats(&y, y1, n, anAmplitudes[z]);

C

void sumFloats(float * y, const float * x, const int yc, const float a) {
    simd_float4 theA = simd_make_float4(a,a,a,a);
    simd_float4 * theY = (simd_float4*)y;
    simd_float4 * theX = (simd_float4*)x;
    assert( (yc&0x3) == 0 );
    for( int t = 0, theYC = yc >> 2; t < theYC; t ++ ) {
        theY[t] += theA * theX[t];
    }
}

我的理解是数组不能保证连续的内存块，因此在调用C代码时必须进行一些转换，我可以通过使用ContiguousArray来解决此问题，但不能使用ContiguousArray来解决。打电话给C。

Answer 1

withUnsafe(Mutable)BufferPointer()可用于获取指向数组（可变）存储的指针，而withMemoryRebound()可作为Float的数组访问float4的数组：< / p>

func sumFloats(y: inout [Float], x: [Float], yc: Int, a: Float) {
    let theA = simd_float4(a, a, a, a)
    x.withUnsafeBufferPointer {
        $0.baseAddress!.withMemoryRebound(to: simd_float4.self, capacity: yc / 4) { theX in
            y.withUnsafeMutableBufferPointer {
                $0.baseAddress!.withMemoryRebound(to: simd_float4.self, capacity: yc / 4) { theY in
                    for t in 0..<yc/4 {
                        theY[t] = theA * theX[t]
                    }
                }
            }
        }
    }
}

示例：

let x: [Float] = [1, 2, 3, 4, 5, 6, 7, 8]
var y: [Float] = [0, 0, 0, 0, 0, 0, 0, 0]

sumFloats(y: &y, x: x, yc: 8, a: 2.0)
print(y) // [2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0]

Answer 2

看看苹果如何定义vForce函数，Martin R的答案可以简化为；

func sumFloats(y: UnsafeMutablePointer<Float>, x: UnsafePointer<Float>, yc: Int, a: Float) {
    let theA = simd_float4(a, a, a, a)
    x.withMemoryRebound(to: simd_float4.self, capacity: yc / 4) { theX in
        y.withMemoryRebound(to: simd_float4.self, capacity: yc / 4) { theY in
            for t in 0..<yc/4 {
                theY[t] += theA * theX[t]
            }
        }
    }
}

，仍然可以使用[Float]参数以相同的方式调用它。

在Swift中将[Float]投射到[simd_float4]

2 个答案: